1. Field
The embodiments relate to a process for producing a coating on a workpiece by cold gas spraying, in which process a cold gas jet containing particles of a coating material is directed at the workpiece and the workpiece is simultaneously irradiated with electromagnetic radiation.
2. Description of the Related Art
A process of the type indicated in the introduction is known, for example, from DE 10 2005 005 359 A1. In this process, the particles accelerated with the cold gas jet toward the surface of a workpiece to be coated are acted upon by an amount of energy (kinetic energy) which does not suffice, per se, to bring about permanent adhesion of the particles on the surface. Instead, this requires an additional introduction of energy into the coating being formed on the workpiece. This introduction of energy takes place via a laser, the radiation of which is focused exactly at that point at which the cold gas jet impinges on the workpiece.
In principle, the process described can also be used to produce catalytic coatings. For this purpose, it is necessary to select particles with a surface which brings about the desired catalytic action. By way of example, it is possible to produce coatings from a photocatalytic material such as titanium dioxide. In order to improve the catalytic action, it is also possible to use nitrogen-doped titanium dioxide (or titanium oxynitride).
According to DE 10 2004 038 795 B4, it is also known to produce catalytic coatings by means of cold gas spraying. In this context, an oxidic powder is applied to a polymer surface by means of cold gas spraying and forms a mechanically firmly adhering coating. In this case, the photocatalytic properties of the oxidic powder are retained. According to DE 10 2005 053 263 A1, photocatalytically active coatings can also be applied to metallic surfaces by means of cold gas spraying. Since the particles are heated only slightly during cold gas spraying, it is also possible to use modified photocatalytic materials, where the modification is retained in the applied coating. By way of example, a powder containing doped titanium oxide can thus be used. Process parameters for producing titanium dioxide coatings by means of cold gas spraying can also be gathered from Chang-Jiu Li et al. “Formation of TiO2 photocatalyst through cold spraying” Proc. ITSC, May 10-12, 2004, Osaka, Japan.
In order to obtain particles of a nitrogen-doped titanium dioxide, it is also possible, however, to employ a sol-gel process, where titanium dioxide powder is melted at high temperatures in gaseous ammonia. Oxidation of titanium nitride also makes production possible. Another possible way is by ion implantation, magnetron sputtering or PVD processes. The titanium dioxide coatings can be doped with a nitrogen content of 2 to 4.4% using the processes. The production of photocatalytic materials such as nitrogen-doped titanium dioxide therefore requires a certain outlay. Processes of this type are described, for example, in Nitrogen-Doped Titanium Dioxide: An Overview of Function and Introduction to Applications, Matthew Hennek, Jan. 20, 2007, University of Alabama.